The IPCC Assessment Process

July 15, 2007

The IPCC was established by governments in 1988 to provide assessments of available scientific and technical information on climate change. The process used to produce these assessments is designed to ensure their high credibility in both science and policy communities. Government involvement is limited to the initial stage to provide a mandate for the work, to participation in the second of two reviews, and to the final stage to ensure that policymakers understand the key findings.

Prior assessments were published in 1990, 1995 and 2001. There are three "Working Groups" examining the physicalscience of climate change; the effects of climate change on nature and society; and the methods for adaptation to and mitigation of climate change. This article discusses only the findings of Working Group I.

Lead authors (LAs) of the report are nominated by governments, with selection based on evidence of active participation in relevant research, and taking into consideration the need for balanced views as well as geographic, gender and age balance. IPCC rules are clear that the content of the chapters is at all times controlled by the LAs. They are asked to assess the relevant peer-reviewed literature and to provide a balanced summary of the present state of scientific knowledge and uncertainty.

The authors' assessment is tested against views in the broader expert community through an extensive review process. Over 600 experts provided more than 30,000 comments on the first two drafts, and independent review editors ensure that all comments are appropriately considered. Thus, whereas the authors are responsible for the final report, the process ensures that it is firmly based on peer-reviewed scientific literature and takes account of the full range of expert views. The publication deadlines for inclusion of recent scientific literature were chosen to ensure complete transparency in the review process and the final deadline was July 24, 2006.

Completion of the Summary for Policymakers (SPM) is done with government delegates in a line-by-line approval process to ensure that language used to express the key findings of the report is clear to policymakers. Such clarifications more succinctly and accessibly communicate the science. The scientists are present to ensure scientific accuracy and consistency with the underlying report. Any changes to the SPM must remain consistent with the underlying chapters and cannot change the authors' assessment of likelihoods or confidence levels. For example, in the SPM statement that most of the warming since the mid-20th century is "very likely due to the observed increase in human-induced greenhouse gas concentrations," the wording very likely is the final assessed view of the relevant authors. As such it could not have been changed in the government approval process to either a stronger or weaker term.